We were just BURSTING to tell Daddy Richard how good it was. Particularly since Daddy Alex could say it was good and then I could say it was good and then Daddy Alex could say it was good and then I could say it was good and then…

You could say that Russell has written a very Moffat script, based around a simple (and invisible) monster drawn from childish games. And yet this is in no way a Moffat story, with no convoluted time structures, no cunning twist ending and the drama being drawn solely from character rather than situation.

"Hell," Sartre tells us, "is other people." And the Doctor certainly discovers that when trapped, like Sartre's (smaller) cast of characters, in a room with "No Exit". (And when the door is opened, no one wants to go though it!) Everything may start perfectly jollily, with the Doctor doing his Doctor thing of chatting to all of the other passengers and getting them to open up and laugh along with him. But there is a dark side to human nature and fear is the tool to uncover it.

It all goes very William Golding, and you almost expect the human pack to start chanting "Kill the Pig! Kill the Pig!" (in unison, of course).

The monster turns out to be almost irrelevant, if it even exists at all, and the Doctor is left deeply wounded by the way his beloved humans have turned on him like rats. Russell admits in the accompanying Confidential that it is also an answer to his own "Voyage of the Damned", the delicious Christmas turkeystuffed with disparate, fragrant characters bonding under stress. Here, things fall apart.

Separating the Doctor from Donna for this story is very clever, and not just for the logistics of filming fourteen (fifteen in fact) episodes without killing your lead actors. Taking away his companion is very much the first step in taking away the Doctor's voice, taking away his identity. Like a god with no one to believe in him, he is weakened by being alone.

And to take the tenth Doctor's voice is a particular cruelty; his verbosity and linguistic prestidigitation are as defining of his character as the boggling stare was for the fourth, the bombast for the sixth or the amnesia for the eighth. If you had to sum him up, you would say that he's the Doctor with all the catchphrases. "I'm sorry; I'm so sorry." "Allons-y!" "No. No, don't do that." "Molto Bene!" The tenth Doctor has been repeating himself for ages; no wonder he's so undone by someone else doing it back at him.

And yet, it's those very verbal tics that save him too. When they come tripping out of Sky Silvestry's possessed mouth, they give her away as the real villain.

Assuming, of course, she really is possessed and not just diabolically dangerous and off her nut.

A lot of what happens here is so reminiscent of a poltergeist haunting: the tapping, the objects thrown around, the scary voices. The usual pseudo-scientific explanation of poltergeist activity is that rather than a genuine external spirit, it is the latent psychic talent of someone very much alive being activated by some trauma – often a teenage (i.e. hormonally charged) girl gets the finger pointed, but anyone under extreme stress could be the one.

It's a tour de force performance from Russell's old mate Lesley Sharp. Initially she's interesting in the way that she makes Sky so cold and stand-offish, even when opening up to the Doctor. It's a performance that hints at secrets – and note the inconsistencies in Sky's story: she tells the Doctor that she was dumped and her partner left for a distant galaxy, but she's the one who is travelling and when terrified her fear is that her ex would come to get her.

This is actually one of Russell's idées fix idées fixes. In "everyday" drama it is quite common to understand that not everyone tells the truth all the time, that the characters are fallible and unreliable and the audience needs to remember to compensate for that. And yet in science fiction, we tend to assume that what people tell us is true. (Of course, the reason for that is that we are trying to build a picture of the world and we don't necessarily have anything against which to judge the truth value of statements when we don't even know what colour the sky is meant to be.) But Russell likes to toy with that, have characters in unreal settings still behave as though it's Albert Square and not the planet Midnight.

Notice that we actually see the Doctor lie. He tells several lies, in fact, not just his usual psychic paper "I can go anywhere" fibs. He tells everyone in the cabin that everything is going to be fine, even though he's been in the cockpit and knows that there is no explanation for why they've stopped. And, of course, he lies about his name, which – when you're talking identity – is about as fundamental a lie as you can get.

And other characters lie too. We automatically filter the bland platitudes of the hostess, but remember the way that Doctor Hobbes is constantly bluffing people that he knows what he is talking about, or that after the events Val Cane says "I said it was her" – a blatant untruth. (And earns the Doctor a "Best ever 'giving her evils' seen in Doctor Who" award as a result!)

So bear in mind that we can't really be sure what Sky Silvestry's real back story is. We don't know what she's running away from and she could be cause as much as victim here.

(The only thing counting against that is the "shadow" that Trainee Engineer Claude thinks he sees from the cockpit. If that is real, then you might argue that it's all the Doctor's fault for opening the windows and letting the mimic be seen and by inference see in return. But, no, because "something" has already somehow stopped the truck. Mind you, their journey takes them through the Winter Witch Canyon – or possibly doesn't: Driver Joe's dialogue seems to contradict the map on screen – which once again both suggests the supernatural and points the finger at the very-Wicca-named Sky.)

But then she is almost the last word in creepy from the moment the lights come back on after the crash. Lesley Sharpe does that same thing that Derek Jacobi did last year when the Professor became the Master, that little change of the body language to say "I'm evil now". And by the climax, her apotheosis with the Doctor's voice spilling from her mouth, she's almost sensuously loving it, the power of the spoken word driving the other people to chaos, horror and murder. She is the devil and she does the devil's work. As much as an answer to "Voyage of the Damned" this is a reply to "The Satan Pit" too; this is the sort of conclusion that that story should have had.

Speaking of the Devil, Professor Hobbes, suggests to me Hobbs (Hob's) Lane from "Quatermass and the Pit", a place where unseen aliens caused human telekinesis to run amok. (Though in fairness, Alex thought of "Nasty, brutish and short" as Hobbes' critique of lifeapplies equally to the humans trapped with the Doctor here.) In the same vein, the Cane family, of course, are reminiscent of the Biblical first murderer, who betrayed his brother.

In a story about words and language, names are clearly important: the Doctor's refusal to give his own real name gets him deeper into trouble, and things are underlined by the revelation that nobody bothered to ask the hostess her name. Along the way we have the Doctor trying to form an (ill-advised) bond with a woman named Sky, just after discovering a woman named River in his future and with a woman named Rose shouting at him from the screen behind his back. Presumably Miss Fire is on her way.

The Doctor is normally like the TARDIS: no, not "square" and "blue"; he manages to blend in. Even without waving the psychic paper around he always usually manages to convince people to trust him. But – again like the TARDIS – that's a disguise, a lie if you like. It's long been suspected, particularly in the New Adventures, that this is something that he does, either by doing something Time Lord-y to the local probabilities or through the old telepathic circuits. But whether it's a Time Lord super-power – in his "biodata" if you're "Mad" Larry – or a part of the TARDIS or just natural charisma, here we see that talent unravelling.

It's not that he's an amateur; as a Time Lord he's a professional at this. But whatever he encounters here, it, whatever "it" is, is a natural. Or maybe, even worse, it is as he feared learning from him and mimicking his ability to control how the humans around him perceive and relate to him.

The story's roots go back to the Classic Series. Doctor Who Confidential cites "The Deadly Assassin" (for the Doctor without companion story), and who wouldn't – it's not just David Tennant's favourite story; it's Alex's as well. (Mine is "The Curse of Fenric" and there's quite enough of that in the mix too!) But whatever Confidential says, it's obvious that it's much more similar to "The Edge of Destruction" aka "Inside the Spaceship". Even superficially it's true, with the claustrophobic all-in-one-set location (with food machine and doors that open onto white void). But much more than that: both "The Edge of Destruction" and "Midnight" are exercises in paranoia, where fears real and imagined drive ordinary people to behaving in terrible ways. When they need to pull together, all they can do is fall apart, and words which should be their allies serve only to make them more afraid. They even share the key moment of psychological horror: "it could have gone into one of us". This is, almost by definition, talky.

It is an "impossible" play – you'd never be able to do the synchronous speeches or the repetition of the root of pi for real – and yet, and here we come back to Sartre, it's very much an eight-people-on-a-set set piece. The direction – Alice Troughton, no relation – is excellent, selling the illusion of sounds moving around the cabin by shifting of camera angles; using quick cuts from the rest of the cast to Lesley Sharp and back to play up the repetition. But this is an actor's piece, it's all about drawing out those emotions; feeling that journey; suffering and learning with the characters.

And like the violin concerto that requires a virtuoso, this script calls for all of David Tennant's talents.

It is, of course, a magnificent piece of work by Tennant. Alex says that the thing that he does best is suffer, and does he ever give us suffering here, broken and voiceless but still not giving in, fighting to hold on to one more second even if it's by catching his foot on a chair to make it a moment more difficult to drag him out. And in one of the most downbeat conclusions of the new series, he is a hollowed out Doctor, no longer filled with the joy in words that began him, bubbling with language back in "The Christmas Invasion".

Last thought: is it really just a coincidence that the Doctor was on he way to see a Sapphire Waterfall… that would be a cascade of Blue Crystals…

Next time… All the prophesies are coming true: Rose is returning; the Doctor's song is over; and… OHMYGOD is that a Metebelis Spider?! The Doctor has stopped and every star is going dim. "Turn Left".

PS:

Outpost Gallifrey comes up TRUMPS with the question: "How would any of the OTHER Dr Whos have survived on Midnight?" My particular favourite answer was the suggestion that the monster would simply EXPLODE when it tried to repeat Mr Doctor Sylv saying "rrrrrrround the rrrrrrugged rrrrrrocks the rrrragged rrrrrrascal rrrrrrraaaaan!!!!"

My only big disappointment was that, due to my LesleyLove, I half-wanted a Utopia-style surprise reveal, whereby the invader shifts across from Sky to the Doctor but he sneaks out into Sky. Sharp would make an astonishingly good Doctor, and unless I claim the Maxil Imperative, I can no longer hope she'll ever get the role. (The same goes for Nina Sosanya but twice as cruelly, considering the duff script she was given.)

You're so right to call it an impossible play; we've come to expect so little from TV drama, but Davies has so much respect for the medium - he uses all the strengths of theatre in a form that could ONLY be done on the telly.